For the operation of air nozzle looms it is generally known that the transport of the weft thread through the insertion channel in the reed and, here especially, the insertion time or speed needed for the weft thread insertion are dependent on several factors. Thus, for example, there are differences in the air effectiveness of the threads coming even from one and the same thread supply. There are variations in the winding density of the thread supply. These variations also have their influence on the weft thread insertion. More specifically, the weft threads of the upper thread layers on a bobbin have a less advantageous surface structure for the air effectiveness than the middle and inner layers of the thread supply. These adverse influences should be removed or compensated by a corresponding operational sequence during the weft thread insertion in the loom.
In order to be able to compensate for these shortcomings and to guarantee the insertion time or speed of the weft thread that is preset in the program control for a weaving cycle, methods are known which influence the insertion time or the speed of the weft thread by increasing or lowering the air impulse duration through the main nozzle of an air nozzle loom. A method for accomplishing such a control by the participation of the relay nozzles in the control or by using the relay nozzles themselves for the control is not known.
German Patent Publication DE-OS 3,818,766, corresponds to U.S. Pat. No. 5,031,672 (Wahhoud et al.), issued on Jul. 16, 1991. The disclosure of Wahhoud et al. is incorporated herein by reference. Wahhoud et al. control the relay nozzles in an air nozzle loom in such a way that different yarn qualities can be used for the weaving in consecutive working procedures. For this purpose, the relay nozzles are controlled in groups and the duration of the impulse length of the controlling is regulated depending on the air effectiveness of each yarn to be worked. Influences that are effective during the transfer of the weft thread from one thread supply bobbin onto another supply bobbin, and which affect the weaving process negatively, cannot be eliminated by this known method.
These shortcomings also arise in the same manner when weaving threads having the same quality, which are however, pulled off from two different but connected thread supply bobbins. Further adverse influences arise, namely those that occur if the first thread supply bobbin from which the weft thread is now being pulled comes to an end and a transfer is made to the next thread supply bobbin, whereby the thread end of the supply bobbin that is running out is connected to the beginning of the thread of the full supply bobbin.
Although, as explained above, the weft thread quality is assumed to be the same for all bobbins, the influences that result from the thread transfer cannot be removed easily through the known relay nozzle control. For such a control it would be necessary to establish for the individual relay nozzles or groups of relay nozzles, a new travelling field or travel pattern in accordance with a respective program and to maintain the new travelling field by supplying a comparatively higher pressure, namely to satisfy a higher energy requirement that must be applied to transport the weft thread. Thus, the once preset insertion parameters for the weft thread would have to be changed, which would not be without influence on the productivity or efficiency of the loom. Further, this measure would cause an undesired high consumption of insertion fluid, which is unacceptable.